Vegetable materials which contain protein are commercially processed to produce vegetable protein materials such as vegetable protein concentrates and vegetable protein isolates. Commonly produced vegetable protein materials include soy protein concentrates, soy protein isolates, pea protein materials, and protein materials derived from legumes. Vegetable protein materials are widely used in the food industry as protein enrichment ingredients or as functional ingredients in a wide variety of foods. For example, vegetable protein materials are used in such food products as meats, nutritional beverages, soups, cheeses, bakery products, and yogurts.
Several varieties of vegetable materials containing protein also contain phytoestrogenic isoflavones in their native, unprocessed state. Isoflavones are phenolic compounds occurring naturally in numerous types of plants which serve to aid in the fixation of nitrogen in the root systems of certain plants, and to act as a natural protectant against parasites.
In the production of vegetable protein materials such as vegetable protein concentrates and vegetable protein isolates for use in foods, the focus has been to obtain a material which is comprised primarily of protein. In the production of vegetable protein materials from vegetable materials containing protein and isoflavones, a substantial portion of the isoflavones are separated from the vegetable protein, resulting in a protein rich material which has been depleted in isoflavone content. For example, vegetable protein concentrates are formed by washing a vegetable material with an aqueous alcohol or an aqueous acidic solution having a pH at about the isoelectric point of the protein. See, e.g., Soy Protein Products, Characteristics, Nutritional Aspects, and Utilization, pp. 3-6 (Pub. Soy Protein Council, 1987). The aqueous acid or alcohol wash removes materials soluble in the wash, including a substantial portion of the isoflavones and carbohydrates in the vegetable material, from protein and other insoluble materials such as vegetable fiber materials, leaving a protein concentrate material which contains from 65% to 90% protein by weight, but which is significantly reduced in isoflavone concentration.
Protein isolates are formed by extracting a vegetable material containing protein with water or an aqueous alkaline solution to solubilize protein and other materials soluble in the aqueous solution such as carbohydrates and isoflavones. The extract containing solubilized protein is separated from insoluble vegetable fiber material, and then the pH of the extract is adjusted to about the isoelectric point of the protein to precipitate the protein. The protein is then separated from the extract and the materials still soluble in the extract, including a substantial portion of the isoflavones, to form a protein isolate material containing 90% or more protein by weight. The protein isolate is washed with water to further remove water soluble materials from the protein. See, e.g., Soy Protein Products, Characteristics, Nutritional Aspects, and Utilization pp. 3-6 (Pub. Soy Protein Council, 1987). The resulting protein isolate is significantly reduced in isoflavone concentration relative to the vegetable material from which the protein isolate is derived.
Removal of isoflavones from vegetable protein materials in the production of protein concentrates and vegetable protein isolates has been an objective in processing of such materials, since isoflavones have been associated with the bitter taste of vegetable protein materials such as soy. For example, Japanese Patent No. 59-232052A teaches a process for removing isoflavones from a soybean protein material by contacting the protein material with an adsorbent resin to produce a better tasting soybean protein. Alcohol extraction of vegetable protein materials to remove alcohol soluble components from the protein is particularly preferred since alcohol extraction produces a better tasting vegetable protein material than aqueous extraction, in part because alcohol is quite effective in removing isoflavone compounds from the vegetable protein material. See, e.g., Japanese Patent No. 63-245,648A.
Isoflavones, however, have recently been implicated as compounds which are responsible for several health benefits in humans. It has been suggested that isoflavones may be effective to prevent or retard certain cancers such as prostate cancer and breast cancer, as described in the following articles: Genistein Inhibition of the Growth of Human Breast Cancer Cells, Independence from Estrogen Receptors and the Multi-Drug Resistance Gene. Peterson and Barnes, Biochemical and Biophysical Research, Communications, Vol. 179, No. 1, pp. 661-67 (Aug. 30, 1991); Genistein and Biochanin A Inhibit the Growth of Human Prostate Cancer Cells but not Epidermal Growth Factor Tyrosine Autophosphorylation, Peterson and Barnes, The Prostate, Vol. 22, pp. 335-45, (1993), and Soybeans Inhibit Mammarm Tumors in Models of Breast Cancer, Barnes et al., Mutagens and Carcinogens in the Diet, pp. 239-53 (1990). It has been postulated that the low incidence of breast cancer in Japanese women is due to a diet which contains large amounts of isoflavones. Soybean Phytoestrogen Intake and Cancer Risk, Herman et al., First International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, pp. 757S-770S (Feb. 20-23, 1994). Isoflavones are also believed to reduce or prevent menopausal symptoms. Dietary Phyto-oestrogens and the Menopause in Japan, Adlercreutz et al., The Lancet, Vol. 339, p. 1233 May 16, 1992). Furthermore, isoflavones have been identified as vasodilating agents in humans and in non-human primates, with corresponding cardioprotective effects. Enhancement of Coronary Vasodilation by Soy Phytoestrolens and Genistein, Honore et al., Circulation, 92:1:349 (1995).
Recent efforts to obtain the medical benefits of isoflavones have focused on separating and recovering the isoflavones from plant materials. The following patents describe various methods of separating isoflavones from plant materials such as pueraria lobata, legumes, and soy: U.S. Pat. Nos. 4,428,876; 5,702,752; 5,679,806; 4,390,559; 4,366,248; 4,366,082; 4,264,509; 4,232,122; 4,157,984; Japanese Patent Nos. 1-258669A; 5-170756A; 41-90720A; 62-126186A; 62-126185A; and PCT patent application No. WO 93/23069. The separated isoflavone materials may be utilized in pharmaceutical or dietary supplement compositions as described in U.S. Pat. Nos. 5,516,528; 5,424,331; 5,569,459; 5,654,011 and PCT patent application No. WO 93/23069.
While purified isoflavone compositions may be useful in pharmaceutical compositions and dietary supplements to treat and prevent a variety of conditions, recent studies indicate that some health benefits available from vegetable protein materials containing substantial amounts of isoflavones cannot be provided by the isoflavones alone or the vegetable protein material when the vegetable protein material is substantially depleted of isoflavones. Ingestion of soy protein materials containing substantial amounts of isoflavones has been shown to reduce the significant coronary heart disease factors total cholesterol and low density lipoprotein cholesterol (LDL-cholesterol) in non-human primates, where it is postulated that the soy isoflavones are responsible for up to 70% of the hypocholesterolemic effect, and appears to have the same effect in humans having elevated levels of cholesterol. See, e.g., s; Meta-Analysis of the Effects of Soy Protein Intake on Serum Lipids, Anderson et al., N. Engl. J Med., Vol.333, No.5, pp. 276-82 (1995). Ingestion of tablets containing isoflavones purified from soy, however, has been shown to have no effect on total cholesterol and LDL-cholesterol in menopausal and perimenopausal women. Soy Isoflavones Improve Systemic Arterial Compliance but Not Plasma Lipids in Menopausal and Perimenopausal Women, Nestel et al., Arteriosclerosis, Thrombosis, and Vascular Biology, Vol. 17, No. 12 (Dec. 1997). Likewise, alcohol extracted soy protein, which contains minimal amounts of isoflavones, has been shown to have little or no effect on total cholesterol and LDL cholesterol. Anthony.
Efforts have also been made to maximize the health benefits from isoflavones remaining in processed vegetable protein materials such as a vegetable protein concentrates or a vegetable protein isolates by converting the isoflavones remaining therein to their most biologically active form. For example, U.S. Pat. No. 5,637,562 provides a process for producing an aglucone isoflavone enriched vegetable protein concentrate in which isoflavone glucosides are converted to the more biologically active aglucone isoflavone by enzymatic cleavage of a glucoside moiety from the isoflavone glucosides. PCT Patent Application No. PCT/US94/10697 discloses a process for producing an aglucone isoflavone enriched vegetable protein isolate by converting isoflavone glucosides to aglucone isoflavones prior to precipitating a protein material from an extract containing soluble protein and isoflavones.